1. Field of the Invention
The present invention relates to a shading device for use in an optical system and also to an optical device equiped with the shading device. More specifically, the invention relates to a shading device for blocking only sagittal rays and also to an optical device equipped with the shading device.
2. Description of the Prior Art
One means conventionally adopted to remedy aberrations of a lens is to place a stop having a circular or substantially circular hole in a plane perpendicular to the optical axis of the lens, the center of the stop being located on the optical axis (for example, see "Introduction to Optics", Vol. 1, p. 123, published by Asakura-shoten, Japan).
Many kinds of lenses including Gaussian lenses exhibit very large sagittal ray aberration. In order to reduce the aberration, a circular stop has been inserted in the optical axis to reduce the aperture, for blocking sagittal rays. However, this stop has the disadvantage that the reduction in the aperture results in a corresponding amount of axial and meridional rays being blocked.